Continuous cathode sputtering system

ABSTRACT

Apparatus for coating substrate members by sputtering comprises a sputtering chamber having two circular cylindrical tubes of insulating material connected together in axial alignment by a metal ring carrying sputtering electrodes and connections for the sputtering voltage, a source of sputtering gas, and a source of coolant. Vacuum-tight ports are provided at both ends of the sputtering chamber, with means for heating, in a vacuum, the substrates to be coated prior to their admission into the sputtering chamber, and means for cooling such substrates, in a vacuum, prior to their removal into the atmosphere. The substrates are transported through the sputtering chamber by means of a conveyor device. The apparatus provides for the rapid manufacture of thin-layer electrical circuits formed by sputtering metallic material on the insulating substrates.

Unite States Cirltler et a1.

tet 11 1 Dec. 3, 1974 1 CONTINUOUS CATHODE SPUTTERING SYSTEM [73]Assignee: Siemens Aktiengesellschaft,

Berlin-Munich, Germany 22 Filed: Oct.30, 1973 21 Appl. No.: 411,088

[30] Foreign Application Priority Data Continuous Parallel-Plate RFSputtering System, by

Byrne et al., IBM Technical Disclosure Bulletin, vol.

13, No. 4, September 1970, pp. 1034-1036.

Practical Design Aspects of a Continuous Vacuum RF Sputtering Machine,by Williams et al., The Journal of Vacuum Science and Technology, Aug.13, 1969, pages 278-281.

Primary Examiner-John H. Mack Assistant Examiner-Wayne A. LangelAttorney, Agent, or Firm-Hill, Gross, Simpson, Van Santen, Steadman,Chiara & Simpson 5 7] ABSTRACT Apparatus for coating substrate membersby sputtering comprises a sputtering chamber having two circularcylindrical tubes of insulating material connected together in axialalignment by a metal ring carrying sputtering electrodes and connectionsfor the sputtering voltage, a source of sputtering gas, and a source ofcoolant. Vacuum-tight ports are provided at both ends of the sputteringchamber, with means for heating, in a vacuum, the substrates to becoated prior to their admission into the sputtering chamber, and meansfor cooling such substrates, in a vacuum, prior to their removal intothe atmosphere. The substrates are transported through the sputteringchamber by means of a conveyor device. The apparatus provides for therapid manufacture of thin-layer electrical circuits formed by sputteringmetallic material on the insulating substrates. I

15 Claims, 3 Drawing Figures l CONTINUOUS CATI-IODE SPUTTERING SYSTEMBACKGROUND 1. Field of the Invention The present invention relates to asputtering coating apparatus and, more particularly, to such anapparatus with means for providing a continuous flow of substratemembers, so that the apparatus operates in a continuous manner.

2. The Prior Art It is known that thin metallic layers can be producedby means of cathode sputtering within a controlled gas environment, andit is known that the sputtering process is enhanced by an auxiliarydischarge which tends to form ions within the controlled gasenvironment. The auxiliary discharge is sustained by means of a coilplaced around the periphery of the container, adjacent the anode, sothat a so-called ring discharge is produced through the high-frequencyelectromagnetic field created by operation of the coil. With thecontrolled gas environment partially ionized, the discharge supplies theions which are necessary for the sputtering, and the ions areaccelerated toward the cathode within the container. Such apparatus isillustrated and described in German Pat. No. 1,122,801.

Devices are also known in which the sputtering takes place with a ringdischarge in a chamber which is permeated with a high-frequencyelectromagnetic field with the electrodes enveloping the chamber andwith means for cooling the electrodes. Such apparatus is illustrated inGerman Pat. No. 1,515,311.

Other arrangements are illustrated in German Pat. No. 1,690,688, inwhich a d.c. or low-frequency alternating magnetic field is employed, inaddition to the high-frequency electromagnetic field. This field may bealigned in parallel or perpendicular to the highfrequency magneticfield, as shown in German Pat. No. 1,690,689.

SUMMARY OF THE PRESENT INVENTION A principal object of the presentinvention is to provide an apparatus in which the process may be carriedout in a continuous manner.

A further object of the present invention is to provide such apparatusin which an even thickness layer is produced over the entire surface ofthe substrate.

A further object of the present invention is to provide such apparatusin which the substrate is maintained generally in vertical orientationduring coating.

A further object of the present invention is to provide apparatus foraccommodating thermal expansion and contraction of the assembly duringheating and cooling.

Another object of the present invention is to provide an apparatushaving a large surface cylindrical anode encircling the interior of thesputtering chamber, such anode serving as a getter surface for undesiredcomponents of the sputtering gas.

Another object of the present invention is to provide a sputteringassembly in which rod-shaped cathodes are employed.

A further object of the present invention is to provide a mechanism bywhich the amount of sputtering is relatively constant throughout thesputtering chamber.

Another object of the present invention is to provide such a sputteringassembly, with means for generating a low-frequency magnetic fieldaxially aligned within the sputtering chamber, to guide electrons withinthe chamber into spiral paths, to increase the current between thecathode and anode, and to permit a reduction in the pressure of theinert gas atmosphere within the chamber.

A further object of the present invention is to provide a mechanism forminimizing variations in thickness of the coating over the surface ofthe substrate.

A further object of the present invention is to provide a sputteringsystem employing a cylindrical cathode arrangement, with means forestablishing a magnetic field intensity along the length of theelectrode in such a way as to produce a uniform coating thickness.

A further object of the present invention is to provide a sputteringapparatus having a heating chamber adjacent the sputtering chamber and ameans to minimize sputtering in the heating chamber.

These and other objects and advantages of the present invention willbecome manifest upon an examination of the following description and theaccompanying drawings.

In one embodiment of the present invention, there is provided asputtering chamber formed of two glass cylinders joined in axialalignment bya metal ring, said ring providing connections to theexterior of said sputtering chamber for connection to a source ofsputtering gas and to a source of coolant and to a sputtering voltage,means provided at each end of said sputtering chamber for introducing acontinuous series of carriers supporting substrate members, saidsputtering chamber including an electrode array comprising a cylindricalcathode and a disk-like anode, and including means surrounding saidinsulating tubes for producing a highfrequency electromagnetic fieldwithin said chamber, and means for producing'a low-frequency magneticfield within said sputtering chamber inaxial alignment with the glasscylinders.-

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to theaccompanying drawings, in which:

FIG. 1 is a side elevation, partly in cross-sectiom'of apparatusillustrating an illustrative embodiment of the present invention;

FIG. 2 is a transverse cross section of the apparatus illustrated inFIG. 1, taken in the plane II-II; and

FIG. 3 is a transverse cross section of a carrier supporting a pluralityof substrate members, which carrier is employed in the apparatusillustrated in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an illustrativeembodiment of the present invention. The sputtering chamber 5 iscomprised of a pair of glass tubes 51 joined in axial arrangement bymeans of a metal connector 6. The connector 6 supports a flow of coolantby means of a pair of conduits l4, and provides a connection 15 betweenthe electrodes inside the sputtering chamber 5 and a source of d.c.voltage. In addition, a flow of sputtering gas is supplied to theinterior of the sputtering chamber through a conduit 16, which ispreferably equipped with a valve adapted to open or close the conduit16, and provides a certain gas throughput.

An inlet chamber 1 is provided, through which sub strate members areadapted to pass on their way from outside the apparatus into theinterior of the sputtering outer door (not shown), which is closed aftera carrier supporting one or more substrate members is inserted into theinlet chamber 1. The chamber 1 is then evacuated by means of a vacuumpump attached to the chamber 1 by a conduit 2. Preferably, the inletchamber 1 is evacuated to a pressure of approximately 10* Torr.Following suchevacuation, it is flushed with a gas mixture whichcorresponds to the sputtering gas, to minimize as much as possible thepresence of gases other than sputtering gas.

A gate (not shown) interconnects the chamber 1 with a heating chamber 3,and the gate is adapted to be opened to permit introduction of a carriersupporting the substrate members into the chamber 3 from the chamber 1.The chamber 3 is previously evacuated by means of a vacuum pump securedthereto by a conduit 2, so that there is no pressure differentialbetween the chambers 1 and 2 while the gate therebetween is open. Theheating chamber 3 is connected to an end of one of the glass tubes 51 bymeans of a metal bellows 4,

which bellows is adapted to expand or contract in an axial direction inaccordance with the thermal expansion and contraction of the componentsof the apparatus.

A pair of highfrequency coils 12 surround the tubes 51, and the ends ofthe coils 12 are connected to a source of high-frequency current so thata plasma of ionized gas is created and maintained within the interior ofthe chamber 5. An end plate 17 facilitates making a vacuum-tightconnection between the chambers 3 and 5.

A cooling chamber 8 is provided at the outlet end of the sputteringchamber 5, and a metal bellows 4 is provided at that end to interconnecta tube 51 to the chamber 8'. The chamber 8 is normally evacuated bymeans of a vacuum pump connected thereto by a conduit 2, and the chamber8 is constructed in similar fashion to the heating chamber 3. It isconnected by means of a gateto an outlet chamber 10, which isconstructed in the identical manner described in connection with theinlet-chamber 1. The outlet chamber 10 is also evacuated by means of avacuum pump connected thereto. by a conduit 2, and is provided with adoor (not shown) which may be opened in order to withdraw the carriersand the substrate members from the chamber 10.

Both'of the tubes 51 are identical in construction so that no furtherdescription of the right half of the chamber 5 is necessary, it beingthe same as the left half which has been described.

An electrode 52 surrounds the interior of the sputtering chamber 5. Theelectrode 52 is in the form of a hollow circular cylinder, and twoadditional electrodes 54 and 56, both of which are disk-shaped, aredisposed at one axial end thereof. The electrode 52 is provided with aplurality of slots 57, which prevent screening of the high-frequencymagnetic field developed by the coils 12. The electrodes 54 and theparts of electrodes 52 which are opposite to the substrate surfaces areconnected as cathode. The electrodes 56 and the parts of electrodes 52which are placed below and above the substrates are connected as anode.The electrode arrangement employing the disk-shaped electrodes 54 and 56improves the sputtering operation at the ends of the sputtering chamber5, so that a generally constant thickness of coating is applied, even atthe ends of the chamber 5. A rectangularly shaped window 9 (best shownin FIG. 2) is provided in theend plates 17 and in the electrodes 54 and56 to accommodate introduction of the carrier supporting the substratemembers, and the clearance provided by such window is preferably aslittle as possible to enhance a choke or throttling effect in the regionof the window 9. This substantially prevents passage of gas moleculesfrom the heating chamber 3, which may be contaminated with residual gasmolecules entering from the inlet chamber 1 into the chamber 5. Inaddition, the chamber 3 is maintained at a lower pressure than thechamber 5, also to minimize contamination. This is assured by thecontinued evacuation of the chamber 3 by the conduit 2, while gas isintroduced into the chamber via the conduit 16.

A coil 13 is provided at each end of the'sputtering chamber 5, and theends of both coils l3 are connected to a source of low-frequency a.c.voltage, so that a lowfrequency alternating field is created whichpermeates the sputtering chamber 5 in an axial direction.

FIG. 2 illustrates one of the glass tubes 51 in cross section, and thecoil 12 which surrounds such tube. The window 9 is illustrated in-theelectrode 54, and the larger disk-shaped electrode 56 is alsoillustrated; For reasons of clarity, the transport mechanism by whichsubstrate members are carried is not illustrated in FIG. 2.

The electrode 52 is provided with four equally spaced slots 57, asillustrated in FIG. 2. The slots 57 prevent the screening of theelectromagnetic field which is created by the coil 12. Instead ofsputtering from the cathode parts of the electrode 52, a number of rods53 forming the sputtering cathode may be provided inspaced-apartrelationship, parallel to the axis .of the sputteringchamber, and they are'arranged at a relatively short distance inwardlyfrom the cylindrical anode 52. Viewed from the position of the substrateto be coated, the electrodes 53 extend through an arc of about 135,indicated in FIG. 2 by the angle a. The rods 53 are spaced apart by adistance of approximately three times the diameter of the rods.

The electrode 52 is preferably water cooled, by means of a plurality ofwater carrying tubes 55. The tubes 55 are in contact with the exteriorsurface of the electrode 52, in heat-conducting relationship therewith.

A cross section of the transport or conveyor arrangement is illustratedin FIG. 3. A carrier 11 is provided with a roller at its upper end,which is trapped by two elongate rods supported by a bracket 70, theroller 110 being adapted to roll longitudinally relative to the rods.The lower end of the carrier 11 is trapped between two rods supported byanother bracket 70. The carrier 11' and the substrate members 20, whichare secured thereto, are maintained in a general vertical canconveniently be introduced into the chamber and extracted from theoutlet chamber without difficulty.

The-sputtering gas, introduced into the chamber 5 through the conduit16, is preferably an inert gas such as argon.

The sputtering electrodes 53 are mounted by brackets (not shown) on theinterior of the metal connector 6, and are connected to a suitablesource of voltage through the terminal 15. The rod shaped elements 53are easily replaced when necessary simply by disassembling the connectorfrom one of the glass cylinders 51, or by removing one or both of theend plates 17. The voltage source applied to the terminal is preferablypulsating d.c., derived from a single phase ac voltage source by meansof a full wave bridge-type diode rectifier or the like. The auxiliarycoils 13 are preferably connected to a source of low-frequency ac.current,

preferably at about 50 Hz. The field generated by the coils 13 causeselectrons to move in spiral paths, causing an increase in the currentbetween the cathode and anode electrodes. The use of the coils 13 alsopermits operation with a lower pressure within the chamber. The a.c.current is preferably in phase with the pulsating d.c. applied to theterminal 15, so that the most cooperative relation between the electricfield, created by the electrodes 53, and the magnetic field, created bythe coils 13, can be maintained. This is'most effectively accomplishedby employing the same single phase a.c. source for both the coils 13 andthe electrodes 53, although in the latter case, a rectifier is employedto furnish the required pulsating d.c. When the electrodes 53 and thecoils 13 are energized in the manner described above, heating of thesubstrate members by electron bombardment is minimized, since electronstend to be deflected by the magnetic field, and the in-phase ac. currentapplied to the coils l3 prevents any variation in thickness in thecoating which might otherwise result.

The coils 13 are spaced apart along the axis of the assembly by adistance greater than the radius of either coil. Thus, the spacingexceeds that of so-called l-lelmholtz coils. When so spaced, themagnitude of the magnetic field is somewhat less in the centerof thechamber 5 than at the ends, which contributes to a uniform thickness ofcoating applied during the sputtering process.

The use of the disk-like electrodes 54 and 56 also contributes to anevenness of the coating throughout the chamber 5. Preferably thediameter of the cathode 54 is half that of the anode cylinder 52, whilethe disk 56 is approximately the same diameter as the anode 52.

The use of the choke windows 9 permits higher pressure inside thechamber 5 than in the heating and cooling chambers 3 and 8 The pressurein the chamber 5 is preferably on the order of l0"Torr, while that inthe heating and cooling chambers is about lO' Torr. The use of thewindow 9 also results in improved operation by tending to smoothdisturbances produced by diffusion pump which is connected to theconduits 2.

Apparatus has now been described by which substrate members may beuniformly coated by sputtering in a virtually continuous manner, whichbrings about a great increase in the speed and efficiency of thisprocess. In addition, sputtered layers are extremely uniform and do notvary in thickness.

It will be evident that others skilled in the art may make additions andmodifications in the apparatus as disclosed herein, without departingfrom the essential features of novelty thereof, which areintended to bedefined and secured by the appended claims.

When several layers of coating are to be applied, a plurality of thesputtering chambers 5 may be connected together, so the substratemembers pass sequentially through all of them.

What is claimed is:

1. Coating apparatus comprising an input chamber, a heating chamber, asputtering chamber, a cooling chamber, and an output chamber, means forconnecting said chambers in series to permit a substrate member to betransported sequentially therethrough, said sputtering chambercomprising two cylindrical tubes formed of insulating materialinterconnected in axially aligned relationship by a metal connector,means for supporting a plurality of electrodes on said ring in positionto envelop said chamber internally thereof, means on said ring forestablishing a connection between at least one of said electrodes and asource of d.c. voltage, means for evacuating said sputteringchamber,-means for introducing a gas into said sputtering chamber, ahigh frequency coil surrounding said sputtering chamber, and a transportmeans mounted centrally within 4. Apparatus according to claim 2,including means for applying a pulsating d.c. voltage to electrodeswithin said sputtering chamber, and means for applying an ac. current tosaid coils which is in phase with said pulsating d.c. voltage.

5. Apparatus according to claim 2, wherein the distance between saidauxiliary coils exceeds the radius of said coils.

6. Apparatus according to claim 1, wherein said electrodes envelopingthe sputtering chamber comprise two circular cylindrical shell members,one of said members serving as the anode and the other as the cathode,said cathode shell covering an angle of approximately relative to theaxis of the chamber.

7. Apparatus according to claim 6, including a diskshaped cathodeelectrode arranged at an end of said sputtering chamber, the diameter ofsaid cathode disk being approximately half the diameter of said anodeshell.

8. Apparatus according to claim 1, wherein said transport meanscomprises a plurality of carriers supported for axial movement withinsaid sputtering chamber, each of said carriers being adapted to supporttwo pairs of substrate members in back-to-back relationship.

9. Apparatus according to claim 8, wherein each of said carrierscomprises a roller, a substrate member supporting member, and adepending arm, said roller supporting said carrier and said armmaintaining said carrier in a generally vertical orientation.

10. Apparatus accordingto claim 1, wherein said electrodes comprise acircular cylindrical shell connected as the anode of the sputteringsystem, and a plurality of rods spaced inwardly a small distance fromsaid anode and covering an angle of approximately 135 relative to theaxis of the chamber.

11. Apparatus according to claim 10, wherein the distance between thecathode rods corresponds to approximately three times the diameter ofeach of said rods.

12. Apparatus according to claim 1, including a pair of metal bellowsfor interconnecting said sputtering chamber with said heating andcooling chambers, to compensate for thermal expansion and contraction.

13. Apparatus according to claim 1, including means mounted on saidmetal connector for supporting a conduit for introducing an inert gasinto said sputtering chamber.

14. Apparatus according to claim 1, including a choke windowinterconnecting each end of said sputtering chamber with the heatingchamber and the cooling chamber, respectively, said means for evacuatingsaid chamber being connected with said heating and cooling chambers.

15. Apparatus according to claim 1, includingmeans for connecting aplurality of said sputtering chambers in series with each other, wherebyseveral coatings can be successively applied to said substrates.

1. Coating apparatus comprising an input chamber, a heating chamber, asputtering chamber, a cooling chamber, and an output chamber, means forconnecting said chambers in series to permit a substrate member to betransported sequentially therethrough, said sputtering chambercomprising two cylindrical tubes formed of insulating materialinterconnected in axially aligned relationship by a metal connector,means for supporting a plurality of electrodes on said ring in positionto envelop said chamber internally thereof, means on said ring forestablishing a connection between at least one of said electrodes and asource of d.c. voltage, means for evacuating said sputtering chamber,means for introducing a gas into said sputtering chamber, a highfrequency coil surrounding said sputtering chamber, and a transportmeans mounted centrally within said sputtering chamber and adapted totransPort a plurality of groups of said substrates sequentially throughthe center of said sputtering chamber.
 2. Apparatus according to claim1, including an auxiliary coil arranged at each end of said sputteringchamber, and means for connecting a source of a low-frequencyalternating current to said auxiliary coils for creating a low-frequencymagnetic field for permeating the sputtering chamber in an axialdirection.
 3. Apparatus according to claim 2, including means forconnecting an alternating current of 50 Hz to said auxiliary coils. 4.Apparatus according to claim 2, including means for applying a pulsatingd.c. voltage to electrodes within said sputtering chamber, and means forapplying an a.c. current to said coils which is in phase with saidpulsating d.c. voltage.
 5. Apparatus according to claim 2, wherein thedistance between said auxiliary coils exceeds the radius of said coils.6. Apparatus according to claim 1, wherein said electrodes envelopingthe sputtering chamber comprise two circular cylindrical shell members,one of said members serving as the anode and the other as the cathode,said cathode shell covering an angle of approximately 135* relative tothe axis of the chamber.
 7. Apparatus according to claim 6, including adisk-shaped cathode electrode arranged at an end of said sputteringchamber, the diameter of said cathode disk being approximately half thediameter of said anode shell.
 8. Apparatus according to claim 1, whereinsaid transport means comprises a plurality of carriers supported foraxial movement within said sputtering chamber, each of said carriersbeing adapted to support two pairs of substrate members in back-to-backrelationship.
 9. Apparatus according to claim 8, wherein each of saidcarriers comprises a roller, a substrate member supporting member, and adepending arm, said roller supporting said carrier and said armmaintaining said carrier in a generally vertical orientation. 10.Apparatus according to claim 1, wherein said electrodes comprise acircular cylindrical shell connected as the anode of the sputteringsystem, and a plurality of rods spaced inwardly a small distance fromsaid anode and covering an angle of approximately 135* relative to theaxis of the chamber.
 11. Apparatus according to claim 10, wherein thedistance between the cathode rods corresponds to approximately threetimes the diameter of each of said rods.
 12. Apparatus according toclaim 1, including a pair of metal bellows for interconnecting saidsputtering chamber with said heating and cooling chambers, to compensatefor thermal expansion and contraction.
 13. Apparatus according to claim1, including means mounted on said metal connector for supporting aconduit for introducing an inert gas into said sputtering chamber. 14.Apparatus according to claim 1, including a choke window interconnectingeach end of said sputtering chamber with the heating chamber and thecooling chamber, respectively, said means for evacuating said chamberbeing connected with said heating and cooling chambers.
 15. Apparatusaccording to claim 1, including means for connecting a plurality of saidsputtering chambers in series with each other, whereby several coatingscan be successively applied to said substrates.